Move ExportKeyingMaterial to State

Move `ExportKeyingMaterial` from `Conn` to `State`.

conn.go

@@ -355,33 +355,6 @@ func (c *Conn) SelectedSRTPProtectionProfile() (SRTPProtectionProfile, bool) {
 	return c.state.srtpProtectionProfile, true
 }
 
-// ExportKeyingMaterial from https://tools.ietf.org/html/rfc5705
-// This allows protocols to use DTLS for key establishment, but
-// then use some of the keying material for their own purposes
-func (c *Conn) ExportKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
-	c.lock.Lock()
-	defer c.lock.Unlock()
-
-	if c.getLocalEpoch() == 0 {
-		return nil, errHandshakeInProgress
-	} else if len(context) != 0 {
-		return nil, errContextUnsupported
-	} else if _, ok := invalidKeyingLabels[label]; ok {
-		return nil, errReservedExportKeyingMaterial
-	}
-
-	localRandom := c.state.localRandom.marshalFixed()
-	remoteRandom := c.state.remoteRandom.marshalFixed()
-
-	seed := []byte(label)
-	if c.state.isClient {
-		seed = append(append(seed, localRandom[:]...), remoteRandom[:]...)
-	} else {
-		seed = append(append(seed, remoteRandom[:]...), localRandom[:]...)
-	}
-	return prfPHash(c.state.masterSecret, seed, length, c.state.cipherSuite.hashFunc())
-}
-
 func (c *Conn) writePackets(ctx context.Context, pkts []*packet) error {
 	c.lock.Lock()
 	defer c.lock.Unlock()

conn_test.go

@@ -364,33 +364,33 @@ func TestExportKeyingMaterial(t *testing.T) {
 	}
 	c.setLocalEpoch(0)
 
-	_, err := c.ExportKeyingMaterial(exportLabel, nil, 0)
+	_, err := c.state.ExportKeyingMaterial(exportLabel, nil, 0)
 	if err != errHandshakeInProgress {
 		t.Errorf("ExportKeyingMaterial when epoch == 0: expected '%s' actual '%s'", errHandshakeInProgress, err)
 	}
 
 	c.setLocalEpoch(1)
-	_, err = c.ExportKeyingMaterial(exportLabel, []byte{0x00}, 0)
+	_, err = c.state.ExportKeyingMaterial(exportLabel, []byte{0x00}, 0)
 	if err != errContextUnsupported {
 		t.Errorf("ExportKeyingMaterial with context: expected '%s' actual '%s'", errContextUnsupported, err)
 	}
 
 	for k := range invalidKeyingLabels {
-		_, err = c.ExportKeyingMaterial(k, nil, 0)
+		_, err = c.state.ExportKeyingMaterial(k, nil, 0)
 		if err != errReservedExportKeyingMaterial {
 			t.Errorf("ExportKeyingMaterial reserved label: expected '%s' actual '%s'", errReservedExportKeyingMaterial, err)
 		}
 	}
 
-	keyingMaterial, err := c.ExportKeyingMaterial(exportLabel, nil, 10)
+	keyingMaterial, err := c.state.ExportKeyingMaterial(exportLabel, nil, 10)
 	if err != nil {
 		t.Errorf("ExportKeyingMaterial as server: unexpected error '%s'", err)
 	} else if !bytes.Equal(keyingMaterial, expectedServerKey) {
 		t.Errorf("ExportKeyingMaterial client export: expected (% 02x) actual (% 02x)", expectedServerKey, keyingMaterial)
 	}
 
 	c.state.isClient = true
-	keyingMaterial, err = c.ExportKeyingMaterial(exportLabel, nil, 10)
+	keyingMaterial, err = c.state.ExportKeyingMaterial(exportLabel, nil, 10)
 	if err != nil {
 		t.Errorf("ExportKeyingMaterial as server: unexpected error '%s'", err)
 	} else if !bytes.Equal(keyingMaterial, expectedClientKey) {

state.go

@@ -160,3 +160,28 @@ func (s *State) UnmarshalBinary(data []byte) error {
 	}
 	return nil
 }
+
+// ExportKeyingMaterial returns length bytes of exported key material in a new
+// slice as defined in RFC 5705.
+// This allows protocols to use DTLS for key establishment, but
+// then use some of the keying material for their own purposes
+func (s *State) ExportKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
+	if s.localEpoch.Load().(uint16) == 0 {
+		return nil, errHandshakeInProgress
+	} else if len(context) != 0 {
+		return nil, errContextUnsupported
+	} else if _, ok := invalidKeyingLabels[label]; ok {
+		return nil, errReservedExportKeyingMaterial
+	}
+
+	localRandom := s.localRandom.marshalFixed()
+	remoteRandom := s.remoteRandom.marshalFixed()
+
+	seed := []byte(label)
+	if s.isClient {
+		seed = append(append(seed, localRandom[:]...), remoteRandom[:]...)
+	} else {
+		seed = append(append(seed, remoteRandom[:]...), localRandom[:]...)
+	}
+	return prfPHash(s.masterSecret, seed, length, s.cipherSuite.hashFunc())
+}